Cerebrospinal Fluid and

Blood Brain BarrierDR. KARISHMA R. PANDEY

ASSISTANT PROFESSORDEPARTMENT OF BASIC AND CLINICAL

PHYSIOLOGY

Topics 1) Brain ventricular system

2) Cerebrospinal fluid (formation, circulation, aborption and functions)

3) Blood brain barrier• Structure• Functions

The cavities of the brain are known as ventricles and the cavity of the spinal cord is called the central canal.Both spaces are filled with CSF.

500 ml of CSF is formed each day by the choroid plexus in the cerebral ventricles.

Choroid plexus consists of networks of capillaries surrounded by an epithelial layer.

Formation of CSF

500 mL/day

50-70% choroid plexus in the two lateral ventricles

Remainder1) ependymal surfaces of all

the ventricles 2) arachnoidal membranes3) perivascular spaces in

the brain that surround the blood vessels passing through the brain (Virchow-Robin space)

Mechanism of formation of CSF

Composition of CSF and plasma

Circulation of CSF

The CSF is absorbed from the subarachnoid space by the arachnoid villi into the subduaral venous sinuses.

Main driving force: colloid osmotic pressure of plasma, which is 25 mmHg higher than CSF.

Additional force: hydrostatic pressure of CSF is 0.5-5 mmHg higher than subdural venous sinuses.

Absorption of CSF

Functions of CSF 1) It regulates the extracellular environment of nerve cells, as it is in direct contact

with the extracellular fluid of the brain, it helps to provide a stable ionic environment for neuronal function.

2) it acts as a hydraulic buffer to cushion the brain against damage resulting from movements of the head.

3) The brain weighs about 1400 g in air, but in its "water bath" of CSF it has a net weight of only 50 g. The buoyancy of the brain in the CSF permits its relatively flimsy attachments to suspend it very effectively.

4) Removes proteins which has leaked in the interstitial fluid of the brain

5) Homeostatic role: increased hydrogen ions due to local hypoxia --- communicate to the CSF---- transmit the change to chemosensitive respiratoy neurons as well as cerebral blood vessels.

Brain injury: countrecoup phenomenon

Because of inertia

CSF EXAMINATION

Lumbar puncture

CSF pressure measurement

Lumbar CSF pressure =70-180 mm CSF.

Avg normal CSF pressure = 112 mm CSF.

damage the brain (hemorrhage, head injury, inflammation of the aqueduct, or the growth of a tumor)

Meningitis

lumbar puncture --- risky ----- because the sudden release of pressure by the puncture may suck the brainstem downwards.

The raised CSF pressure may be detected during examination of the fundus of the eye. (Monro Kellie doctrine)

Effect of raised CSF pressure

HydrocephalusIncrease in the volume of CSF

Leading to enlargement of cerebral ventricles

Causes: 1) Increased rate of formation of CSF (rare)

2) Reduced rate of absorption of CSF (communicating type)

3) Obstruction to the flow of CSF due to blockage of foramina of Magendie and Luschka (non-communicating type)

If the Fomamina of Magendie and Luschka are blocked the entire ventricular system gets distended.

If the aqueduct of sylvius is occluded : the lateral ventricles and the 3rd ventricles get distended.

If one of the foramina of Monro is blocked: the corresponding lateral ventricle gets distended.

Secretion and Absorption of CSF

Volume of CSF = 150 ml. CSF is replaced about 3.7 times every day.

Blood Brain Barrier Capillaries in the brain do not have pores between adjacent endothelial

cells

tight junctions : 1. endothelial cells of brain capillaries2. the epithelial cells in the choroid plexus

Effectively prevent proteins from entering the brain in adults and slow the penetration of smaller molecules.

This uniquely limited exchange of substances into the brain is referred to as the blood–brain barrier.

Water, CO2, and O2 and lipid-soluble free forms of steroid hormones : easy penetration

Glucose : major ultimate source of energy for nerve cells. GLUT 1

molecules within brain capillaries must be moved through the endothelial cells by diffusion and active transport, as well as by endocytosis and exocytosis

brain cannot obtain molecules from the blood plasma by a nonspecific filtering process

Circum Ventricular Organs: brain areas outside the blood brain barrier

NH:The neurohypophysis,OVLT: organum vasculosum of the lamina terminalis SFO: subfornical organ, AP: area postrema (PI: pineal, SCO: subcommissural organ)

• Capillaries are fenestrated• Allows relatively free exchange between the

plasma and the interstitial fluid of the neural space

Function : • sensory receptors that respond to specific changes

in the body fluids, such as changes in osmolality and in glucose concentration,

• receptors for peptide hormones that regulate thirst, such as angiotensin II.

Functions of BBB1) maintains the constancy of the environment of the neurons

in the central nervous system.

2) protection of the brain from endogenous and exogenous toxins in the blood and

3) prevention of the escape of neurotransmitters into the general circulation.

Clinical Considerations1) BBB presents difficulties in the chemotherapy of brain diseases because

drugs that could enter other organs may not be able to enter the brain.

2) In treating infections such as meningitis, only those antibiotics that can cross the blood-brain barrier are used.

3) BBB is broken down in areas of infection or injury.

4) Tumors develop new blood vessels --- capillaries that are formed lack contact with normal astrocytes--- no tight junctions-----vessels fenestrated---- helps in identifying the location of tumors---- substances such as radioactive iodine-labeled albumin penetrate normal brain tissue very slowly, but they enter tumor tissue----tumor stand out as an island of radioactivity in the surrounding normal brain.

Thank you